A process plant compressor is typically driven by a motor receiving electricity from a central supply system, or by a motor receiving electricity from a generator driven by a gas turbine or other engine, or directly by a gas turbine engine. Cost of equipment and operation, being of prime importance, provides incentive to avoid use of a motor and to drive the compressor with a gas turbine engine. However, the operating speed of the gas turbine engine may not match the operating speed of the compressor. To match speeds, a gear system is required adding some cost and power loss.
Process plant compressors are typically radial compressors having a large diameter bull gear with meshing pinions upon the ends of which compression impellers are mounted. The multiple impellers within their own respective housings provide several stages of compression as desired. The bull gear and its meshing pinions are contained within a common housing. Consequently such compressors are known as integral-gear compressors. The pinions may have differing diameters to best match the speed requirements of the compression impellers that they drive. The compressed air between any two stages is ducted to an intercooler, wherein it is cooled, thereby providing a more efficient compression process. Such compressors are not expensive, but are heavy, require much space and a supply of coolant for the intercoolers. All of these conditions are readily acceptable in a process plant such as a cryogenic air separation plant which requires a large continuous flow of compressed air supplied at minimum cost.
Advantageously, an integral-gear compressor may be driven by a gas turbine engine with its output shaft coupled to the bull gear or to a pinion meshing with the bull gear in the processor. Thus the cost and power loss of an additional gear system is avoided. However still additional improvement is possible by the use of this invention.
Typically a stationary gas turbine engine has been derived from an aircraft gas turbine engine which requires low weight, compactness and small frontal area. Thus typically gas turbine engines have axial compression stages without intercooling in order to achieve these requirements. The mechanical difficulty of extracting compressed air between closely spaced axial stages, cooling it, and reinjecting the cooled air precludes intercooling in axial compressors. The compressor stages in a gas turbine engine are housed within the casing which houses the other components.
Since axial compressors in gas turbine engines are small and do not employ intercooling, their efficiency is lower than that of process plant compressors employing intercooling. For example, intercooling in a compressor with four compression stages providing an overall compression ratio of 7.9, reduces the power required for compression by 20% over that required without intercooling. In a gas turbine engine however, the turbine typically must produce two units of power to drive its compressor for each unit of power delivered through its power output shaft. Thus in a gas turbine engine, 20% increase in compression efficiency results in a 40% increase in power output when some of the heat in the exhaust from the turbine is used to heat the air entering the combustor from the intercooled air compressor. Hence a large improvement in efficiency can be secured by supplying the compressed air required by the gas turbine engine combustor from a process compressor employing intercooling. The process compressor can be sized to provide only sufficient air for the gas turbine combustor, which then can be used as a power producer. The process compressor can be sized to provide more than sufficient air for the gas turbine combustor, the additional air being ducted to a process plant for use therein. A single process compressor may serve to supply more than one gas turbine combustor and compress more than one fluid. Many combinations of the above mentioned uses are possible.
The gas turbine without its integral compressor is basically a combustor and turbine and can be termed a combustor-turbine unit. Existing models of gas turbine engines can be manufactured as combustor-turbine units merely by leaving out the compressor blades, thus saving on fabrication cost.
In a process plant, discharging or intermediate gas streams often are available that can be employed to increase power production, produce refrigeration, reduce fuel consumption or reduce emissions. An available stream of compressed air can be boosted in pressure to the pressure of the combustor in the combustor-turbine unit. Similarly, an available stream of compressed gas with little or no oxygen content can be boosted in pressure and used in the combustor of the combustor-turbine unit as a replacement for a portion of the air normally supplied. An available stream with some fuel content, i.e., a fuel gas stream, can be burned in the combustor thus reducing the amount of primary fuel required. An available steam stream can be injected into the combustor for power augmentation or emission reduction. Available gas streams can be expanded as well as compressed before being discharged or introduced into the gas-turbine unit.
Such streams can be advantageously processed in a machine such as an integral gear compressor fitted with stages to compress one or more gas streams, and additionally, stages to expand one or more compressed gas streams. The energy recovered in the expansion of a gas stream will be transferred directly into compression of another gas stream. Such an integral gear machine, having compression and optional expansion stages, shall herein be termed an integral-gear pressure processor. Thus pressure processing of a gas stream shall mean compression or expansion of the gas stream, and a pressure processing stage shall mean a compression stage or an expansion stage. Integral-gear pressure processors may be employed in combinations to accomplish all of the compression and expansion functions needed.
It is an object of this invention to provide systems and methods for more efficient supply of compressed air or gas for supply to a process plant or other external use.
It is a feature of this invention that a combustor-turbine unit is directly coupled to drive the bull gear of an integral-gear multi-stage pressure processor for supplying compressed air to a process plant and the combustor-turbine unit itself.
It is an advantage of this invention that an integral-gear pressure processor provides machinery of attractive mechanical structure and efficiency to compress and expand multiple gas streams.